Under the 3GPP standards, a ‘NodeB’ (or an ‘eNB’ in LTE) is the base station via which mobile devices connect to a core network and communicate to other mobile devices or remote servers. For simplicity, the present application will use the term base station to refer to any such base stations. Communication devices might be, for example, mobile communication devices such as mobile telephones, smartphones, user equipment, personal digital assistants, laptop computers, web browsers, and the like. 3GPP standards also make it possible to connect non-mobile user equipment to the network, such as Wi-Fi routers, modems, which can be implemented as a part of a (generally) stationary apparatus. For simplicity, the present application refers to mobile communication devices (or mobile devices) in the description but it will be appreciated that the technology described can be implemented on any mobile and “non-mobile” equipment that can connect to such a core network.
The latest developments of the 3GPP standards are referred to as the Long Term Evolution (LTE) of EPC (Evolved Packet Core) network and E-UTRA (Evolved UMTS Terrestrial Radio Access) network. LTE (and more recently LTE-Advanced, or ‘LTE-A’) makes it possible for User Equipment (UE), such as mobile devices to connect efficiently to the core network using alternative, non-3GPP radio access technologies (RAT) as well, for example, using the Wireless Local Area Network (WLAN) standard and the like. The supported access technologies are covered in the 3GPP TS 23.402 standards document (version 13.2.0) titled “Architecture enhancements for non-3GPP accesses”.
3GPP technical report (TR) 36.875 V 13.0.0 describes a so-called ‘LTE-WLAN aggregation’ service for LTE UEs (which can also be referred to as ‘dual radio connectivity’). LTE-WLAN aggregation (LWA) in this case refers to a scenario in which a compatible UE is served, concurrently, both by an LTE base station and a non-LTE base station (such as an access point of a WLAN). LWA may be configured for the UE by the LTE network (e.g. serving base station/E-UTRAN), depending on (measured) signal quality, network load, required quality of service (QoS), movement/location of the UE, and/or the like. The UE facilitates the setting up of an LWA service by providing WLAN measurements on a per access point basis to its serving base station. Based on this, the serving base station selects a number of candidate access points and sends a list identifying the candidate access points to the UE, which selects an access point from the list to provide, in effect, a secondary cell (SCell) for the LWA service. The UE informs the serving base station about its selection.
Once the UE is also connected to the WLAN, it may be handed over between access points of that WLAN, for example, in order to keep serving the UE via the base station that has the most optimum signal quality (for that UE) and/or in order to optimise WLAN performance.
However, when the UE is handed over to an access point that is located at the edge of a particular WLAN and/or at the edge of the cell of the LTE base station currently serving the UE, in some cases the UE may move outside the area served by the WLAN and/or the LTE base station before the serving base station has a chance to de-configure the LWA service for the UE. This may result in a loss of connection at either the WLAN (non-LTE) or the LTE part of the LWA service, and consequently, it may cause failure to meet the QoS required for the UE's communications.
Similarly, failure to meet the required QoS may also happen when the UE is handed over within the WLAN to an access point that is unable to provide the same QoS as the access point from which the handover takes place. In this case, the serving base station will be unable to de-configure (or update) the LWA service for the UE in time, i.e. prior to failure to meet the required QoS.
Furthermore, radio link failure (RLF) may occur on either the WLAN or the LTE part of the UE's LWA service, for example, due to adverse radio conditions such us unexpected interference and/or the like. If such an RLF occurs on the WLAN connection, the above described drawbacks apply (i.e. the LTE base station cannot act timely to maintain the required QoS). On the other hand, if an RLF occurs on the UE's LTE connection, the UE will try to re-establish its radio resource control (RRC) connection with the E-UTRAN, typically with the base station that has the best signal quality. However, in the event of an RLF of the current serving base station, the base station having the best signal quality is almost certainly a different base station to the base station managing the LWA service meaning that a potentially good connection with the WLAN will have to be dropped.
Moreover, as the UE is moving within the coverage of the E-UTRAN, it may be necessary to hand the UE over to a new serving base station. However, handover between (LTE) base stations also requires terminating any connectivity that involves the old serving base station (including termination of the associated WLAN connection of an LWA service) and setting up a new LWA service for the UE under the control of the new serving base station. The inventors have realised that this may result in unnecessary signalling between the UE and the serving base stations and also between the UE and the WLAN, especially when there would otherwise be no need to change the current WLAN access point because the quality of service it provides is sufficient.